Vehicle telematics services carried over a public land mobile network (PLMN) or other wireless carrier system present certain challenges unique to the mobile vehicle application. For example, some vehicle telematics units (VTU) are designed to permit both voice and data communications over the wireless carrier system using one or more of the various available different transmission technologies, such as 2G CDMA (IS-95), 3G CDMA2000 (IS-2000, 1 XRTT, EVDO), 3G UTMS (W-CDMA, HSPA), 2G/2.5G
GSM (GPRS and EDGE). Depending on such things as the technology used, e.g., GSM versus CDMA, the registration or acquisition process required, the frequent movement of the vehicle into and out of a home PLMN (HPLMN), the availability of one data transmission protocol versus another, and the particular type of call being made to or from the vehicle, the VTU may only have one wireless communication protocol available and suitable for use, or may have more than one from which it can select. And while multiple types of wireless transmission may be available at any one time, their associated cost of use can vary making it desirable to judiciously select among them. Similarly, call connection costs associated with data roaming can be significant and it can therefore be desirable to implement connection strategies that minimize roaming and its associated costs.
In a cellular wireless carrier systems, call origination involves connecting with the cellular network and establishing a voice or data connection to the desired endpoint equipment, such as either a telematics service call center or called party's mobile handset or landline. Data connections can be by way of a cellular network voice channel, using data compatible modems at each to exchange data, or via for example, a packet data connection such as are available over GPRS networks. While known techniques for origination of such calls can be used, vehicle telematics-based mobile originated calls present somewhat different challenges than exist for mobile handsets due to, for example, the different types of voice and data calls being placed and the variety of ways in which the VTU is used for data communication. For example, rather than being used only for placing personal voice calls by a vehicle occupant, the VTU can also be used to report data back to the call center, such as GPS data or other vehicle data including diagnostic trouble codes (DTCs) and other vehicle operational information. Some of this data may be sent automatically over a VTU-initiated call without any involvement of the vehicle drive or other occupant, whereas other such data may be desirably exchanged either at the outset or during a voice call used for communication of speech.